1. Field of the Invention
The present invention relates to an apparatus for optically reading an image drawn on the document surface.
2. Prior Art of the Invention
A multi-function printer having the functions of copying machine, scanner, printer, facsimile machine etc. is provided with an image reading apparatus for optically reading an image drawn on the document surface.
The reduction optical system (reduction CCD system) has been well known as the image reading system. This apparatus has an advantage that even if the document is not in contact with the document table, a sharp image can be obtained by setting the focal depth deep. But its disadvantage is that the size is large. For this reason, the contact system in which information from the document is led to a sensor in the same magnification with an erect image as shown in FIG. 17 comes to be used when the size reduction or thickness reduction of the apparatus is needed.
In other words, LED arrays 112 are mounted over document surface 106 in such a way that they are bilaterally symmetrical. And the light sent to document surface 106 is reflected on the surface and received by rod lens array 121 mounted in an upper and middle position over two LED arrays 112.
The LED array 112 has many LED elements 125 mounted on substrate 124 as shown in FIG. 18. The rod lens array 121 has a specific number of cylindrical rod lenses 122 disposed side by side and sandwiched between substrates 124 as shown in FIG. 19.
In such a contact system, the distance between sensor 108 and document surface 106 (hereinafter xe2x80x9cconjugate lengthxe2x80x9d) can be decreased and the whole size of the apparatus can be reduced considerably.
To further reduce the size of the apparatus, it is necessary to further shorten the conjugate length. To further shorten the conjugate length, the diameter of each rod lens 122 has to be reduced. However, the problem is that to reduce the diameter would cause much optical noise such as cross talk and flare light and an image projected on sensor 108 would be unclear.
To reduce the size of the apparatus, it is also important to place the light source near document surface 106 as far as possible. However, the prior art LED array is a set of point light sources and therefore unless this light source and document surface 106 are kept a certain distance away from each other, the illuminating strength can not be kept uniform. That is, the attempt to reduce the size of the apparatus using the prior art LED array is limited.
The present invention has been made in view of the above circumstances, and it is an object of the present invention to reduce the size of the image reading apparatus, and to achieve the object, the following means are adopted.
That is, two light sources are so mounted over the document surface that they are bilaterally symmetrical and kept a certain distance away from each other while forming a certain angle with the document surface. These light sources are surface light emitters made by forming a light emitting layer on a transparent substrate. In the gap between these two surface light emitters, there is provided a fiber lens formed by bundling a plurality of optical fibers.
With those surface light emitters, a uniform illuminating intensity can be obtained at the reading position even if those light sources are brought near the reading position. Furthermore, if a fiber lens smaller than the rod lens in diameter is used, the conjugate length can be shortened. Thus, it goes without saying that it permits the reduction of the size of the apparatus.